Electric discharge apparatus



Jan. 25, 1944.

R. w. PEARSON ET AL 2,340,077

ELECTRIC DISCHARGE APPARATUS Filed May 14, 1942 203 209 I! INVENTOR6 L95 ,/,9/ Faber) M Pea/var) ana dhrmce .B. Jfadum 1.9a BY ATTORNE Patented Jan. 25, 1944 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE APPARATUS Application May 14, 1942, Serial No. 442,940

7 Claims.

This invention relates to electric discharge apparatus and has particular relation to an elec tronic control system for welding apparatus.

In resistance spot welding, highly uniform welds of good quality may be obtained by a method which is known as pulsation or interrupted spot welding. A predetermined number of discrete impulses of current is supplied to the materials to be welded to produce each weld. Each impulse is of a predetermined length and there is a predetermined time interval between successive impulses. Since the welding apparatus is employed in welding a number of different mate rials having varying dimensions and properties, it is necessary that the control system be adjustable over a wide range to vary the length of the impulses as well as the length of the intervals between successive impulses.

A pulsation welding apparatus is shown in a copending application of Robert W. Pearson and S. J. Murcek, Serial No. 412,660, filed September 27, 1941, and assigned to the Westinghouse Electrio 8; Manufacturing Company. In this apparatus, current is supplied from an alternating source through a pair of inversely connected ignitrons to the welding transformer. A contactor of a relay is arranged in the firing circuits of the ignitrons in such a manner that welding current flows only in the half periods in which the relay is energized. A timing system is provided which energizes the relay for a predetermined interval of time and then deenergizes it for another predetermined interval of time. The timing system continues to repeat this energization and deenergization for a preselected period of time.

The apparatus described in the copending Pearson and Murcek application is entirely satisfactory for many purposes. However, it is impossible to determine at what point in a half period of the source the relay will be initially energized. It is therefore, impossible to maintain the current-time product exactly constant which is desirable in certain welding operations.

An interrupted spot welder whose operation is synchronized with the alternating current of the source is described in the copending application of Finn H. Gulliksen, Serial No. 271,951, filed May 5, 1939, Patent No. 2,303,453, December 1, 1942. In the Gulliksen apparatus the welding current is always initiated at the same instant in a half period so that the current-time product remains constant. However, a considerable number of electric discharge devices and other equip-- ment is employed which increases the manuiacturing cost and renders the operation more complex.

It is accordingly an object of our invention to provide an interrupted spot welder synchronized with the source and having a simplified construction and operation.

Another object of our invention is to provide a new and improved timing system for an interrupted spot welder which operates in synchronism with the alternating potential source.

A more general object of our invention is to provide a novel system for supplying power from a periodically pulsating source to a load in discrete impulses, each impulse being of a predetermined length as measured in terms of periods of the source with a predetermined time interval between successive impulses.

More specifically, it is an object of our invention to provide an improved spot welding system for synchronous operation from an alternatingcurrent source which employs a minimum number of electric discharge valves and control circuits.

In accordance with our invention, current is supplied from a source to the welding transformer through a pair of ignitrons connected in anti parallel. Firing of the ignitrons is controlled by a synchronous on-time timing system which includes a start valve and a stop valve. The ontime timing system is conditioned for operation by the energization of a control relay. An auxiliary alternating-current circuit is arranged to energize the control relay as long as an electric discharge control valve in the auxiliary circuit is rendered conductive in each positive half period. The control valve is originally maintained non-conductive by the potential appearing across a first capacitor in the control circuit thereof.

To initiate a welding operation, the first capacitor is discharged, rendering the control valve conductive. The control relay is immediately energized and conditions the on-time timing system for operation. Energization of the relay also causes a biasing potential to be impressed in the control circuit of the control valve. This biasing potential is effective to render the valve conductive in successive positive half periods of the source regardless of the potential of the first capacitor.

The start valve is rendered conductive at the beginning of the next positive half period of the alternating current after the control relay is energized. When the start valve becomes conductive, welding current flows through the ignitrons and is supplied to the welding transformer continuously for a predetermined time interval. At and a rectifying system 53 which impresses a the expiration of the predetermined interval, the stop valve is rendered conductive. When the stop valve becomes conductive, the biasing potential in the control circuit of the control valve is greatly reduced. In the meantime, the first capacitor has been recharged so that when the biasing potential is reduced, the capacitor potential is sufllcient to maintain the control valve non-conductive.

The control relay is deenergized when the control valve does not become conductive in successive positive half periods. A predetermined time after the control relay is deenergized, the first capacitor is again discharged to render the control valve conductive and another current impulse is supplied to the welding transformer. After a predetermined number of current impulses have been so supplied, an overall timing system becomes efiective to prevent furthe energization of the control relay.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, the single figure of which is a diagrammatic view illustrating an embodiment of our invention.

As illustrated in the drawing, current is supplied from a source of alternating current 3 through a pair of ignitrons 5 and 1 connected in anti-parallel to the primary 9 f the welding transformer II. The secondary l3 of the welding transformer is connected across the electrodes i and H in engagement with the material l9 to be welded. Each of the ignitrons includes an anode 2i, a mercury pool cathode 23 and an igniter 25 in contact with the cathode. The ignition circuit of one of the ignitrons 5 may be traced from one side of the source 3 through the primary 9 of the transformer II, the anode 21 and cathode 29 of an electric discharge valve 3! to the igniter 25 and cathode 23 of the lgnitron 5, to the other side of the source 3. The ignition circuit or the other ignitron 1 may be similarly traced through the anode 33 and cathode 35 of another electric discharge valve 31. The electric discharge valves 3| and 31 in the ignition circuits of the ignitrons 5 and 1 are of the arc-like type and are hereinafter designated as the firing tubes.

Conductivity of the firing tube 3! for the first ignitron 5 is controlled by an on-time timing system 39. The control circuit of the firing tube 81 for the second ignitron 1 may be traced from the grid 40 through a grid resistor 4|, the secondary 43 of an auxiliary transformer 45, a biasing potential source 41, to the cathode 85. The primary 49 of the auxiliary transformer 45 is connected directly across the primary 9 of the welding transformer. The arrangement described for control of the firing tube 31 for the second ignitron 1 is what is known as a follow-up system. The first ignitron 5 is rendered conductive initially and when it ceases to conduct, the reactance of the welding transformer primary 9 causes a potential impulse to be impressed in the control circuit of the firing tube 31 through the auxiliary transformer 45. As a result, the second ignitron 1 is rendered conductive.

The on-time timing system 89 is energized from he source 3 through an auxiliary transformer BI ill) direct-current potential across a voltage divider 55. An electric discharge valve 51 of the arc-like type, which is hereinafter designated a start valve, is connected with its anode 59 and cathode 6| between the positive terminal 53 of the voltage divider 55 and an intermediate tap near the negative end through a resisto 61 and a contactor B9 of a control relay 1|.

The control circuit of the start valve 51 may be traced from the grid 13 through a grid resistor 15, a second resistor 11, the lower portion 19 of the voltage divider 55, a conductor BI and resistor 51 to the cathode 6!. The potential across the lower portion 19 of the divider tends to maintain the start valve 51 non-conductive after the contactor 59 of the relay 1| is closed. However, a potential impulse is impressed across the resistor 11 in the control circuit from the source 3 through a phase-shifting circuit 82 and an impulsing transformer 83. This potential impulse counteracts the biasing potential of the lower portion of the divider to render the start valve conductive. The phase-shiftin circuit 82 is preferably so ad justed with respect to the power factor that the start valve 51 becomes conductive at the beginning of a half period of the alternating current but it may be set to render the start valve conductive at any predetermined instant in the half period.

An electric discharge valve 94 of the arc-like type, which is designated a stop valve, is connected between the positive terminal 63 of the voltage divider 55 and an intermediate tap thereof through the contactor 59 of the control relay 1|. The control circuit of the stop valve 84 extends from the grid 81 through a grid resistor 89, a conductor 9|, a capacitor 93, to the lower intermediate tap 55 of the divider. The control circuit continues from the intermediate tap 85 to the cathode of the stop valve. The capacitor 93 is also connected in series with the start valve 51 through a rectifier 91 and a potentiometer 99. Thus, when the start valve 51 becomes conductive, the capacitor 93 is charged at a rate which is determined by the setting or the potentiometer 99. The portion of the voltage divider in the control circuit of the stop valve 84 tends to maintain it non-conductive, but after a predetermined interval of time, the capacitor 93 is charged to a sufficlent potential to counteract the biasing potential of the divider and render the stop valve conductive.

The control circuit of the firing tube 3| for the first ignitron 5 may be traced from the grid Hll through the grid resistor I93, an intermediate tap I 05 on the resistor 51 in the start valve circuit, the lower intermediate tap 65 on the divider, another intermediate tap 85 on the divider, and conductor I81 to the cathode 29 of the firing tube. It is then apparent that when the start valve 51 is non-conductive, the grid IOI of the firing tube 3| is negative with respect to the cathode 29. However, when the start tube 51 becomes conductive, the intermediate tap I05 on the resistor 51 in series therewith and, therefore, the grid I 91 of the firing tube 3| becomes positive with respect to the cathode 29. when the stop valve 84 becomes conductive, the cathode 29 of firing tube BI is connected therethrough to the positive terminal 83 of the divider 55 and the grid i0! again is negative with respect to the cathode 29.

The operation of the control relay 1| is controlled by a timing system indicated generally at I09. Power is supplied to the system I09 from the source 3 through an auxiliary transformer III. A voltage divider H3 having four sections H5, H1, H9 and I2I is arranged to be energized from the secondary I23 of the auxiliary transformer III. A filter capacitor I25 is connected across the two upper sections H5 and H1 of the divider H3, and another filter capacitor I21 is connected across the two lower sections H9 and I2I. The center tap I29 of the divider H3 is connected through a push button switch I32 to one side of the secondary I23. The outer terminals of the voltage divider H3 are connected through rectifiers I33 and I35 to the other side of the secondary I23. The direction of current flow throu h the rectifiers I33 and I35 is such that the capacitor I25 across the two upper sections of the divider is charged in one half period, and the other capacitor I21 across the two lower sections, is charged in the opposite half period. This rectifier-capacitor arrangement is a typical voltage doubler circuit which is well known in the art.

A control capacitor II is connected across the three upper sections H5, H1 and H9 of the divider through an adjustable resistor I34. An electric discharge device I36 of the arc-like type in series with an inductance I31. is connected directly across the control capacitor I3I with its cathode I39 connected to the negative plate of the capacitor. The circuit through the device I36 is controlled by a contactor M! of an other relay I43. The operating coil I45 of this relay I43 is energized from the secondary I23 of the auxiliary transformer III through normally closed contactor I41 of a relay I49 when the push button switch I32 is closed. A pair of holding circuits are connected across switch I32, one through contactor I5I of relay I43 and the other through contactor I53 of relay 1I.

Another capacitor I55 is connected across the three lower sections H1, H9 and I2l of the divider through another adjustable resistor I51. The grid I59 of the discharge device I36 is connected to the positive plate of this capacitor I55 through a grid resistor IBI. Thus, when the capacitor I55 is charged, the grid I59 of the device I35 is positive with respect to its cathode I39, permitting the device to be rendered conductive. However, when the capacitor I55 is discharged, the device I36 is prevented from becoming conductive by the negative poten ial appearing across the lower section I2I of the divider. The capacitor I55 may be discharged through a resistor I63 by the closing of a normally open contact I65 of relay I49 or by the closing of another contact I61 of the control relay H.

The operating coil I1I of the control relay H is arranged to be energized from the secondary I23 of the auxiliary transformer III. The energizing circuit may be traced from one side of the secondary I23 through a parallel circuit consisting of the operating coil I1I on one side and a capacitor I13 on the other side, a current-limiting resistor I15, the anode I11 and cathode I19 of a control electric discharge valve IBI, the center tap I29 of the divider H3, and contactor Nil relay I43 to the other side of the secondary. The control valve IBI is of the arc-like type, and its grid I33 is connected to the negative plate of the control capacitor I3I.

The control circuit of the control valve I3I extends from the grid I83, through grid resistor I36, the control capacitor I3I, sections H and H1 of divider H3 to the cathode I19. Thus, when the control capacitor I3I is charged, the grid I83 is negative with respect to the cathode H9. However, when the capacitor I3I is discharged, the grid I83 becomes positive, permitting the control valve IBI to be rendered conductive in each positive half period of the source 3. The capacitor I13 in parallel with the operating coil I1I of the control relay H is of such dimensions that the coil is maintained energized between successive positive half periods. It is then evident that in the absence of other influences, the control relay TI is energized as long as the control capacitor potential remains less than the biasing potential provided by the two upper sectionsof the divider H3. However, the grid I83 is connected through resistor 2I3, conductor 2I5 and contactor B9 of relay 1| to the positive terminal 53 of divider 55 in the on-time timing system and the cathode I19 is connected by conductor 2I1 to intermediate tap 2I9 on divider 55. Thus, when relai 1| is first energized and closes contactor 59, the potential of portion I34 of divider 55 is placed across the grid and cathode of control valve I8! to render it conductive in successive positive half periods regardless of the potential of control capacitor I3I. Then when the stop valve 84 becomes conductive, the potential between terminal 63 and tap 35 is greatly reduced so that the potential of section I84 is insufficient to maintain the control valve conductive.

An overall timing system I85 is also provided to limit the number of current impulses which may be supplied in one operation. A. voltage divider I91 is connected directly across the secondary I23 of the auxiliary transformer III. A capacitor I89 is then charged by the rectified leaka e current through the grid IBI and cathode I93 of another electric discharge valve 195 of the arc-like type. The circuitfor charging the capacitor I89 may be traced from the center tap I91 01 the divider I31 through the capacitor I89. a grid resistor I99, the grid IBI and cathode I93 of the valve I95 and contactor I5I or the push button switch '32 to one terminal. of the divider. The cathode 193 of the valve I95 is also con nected to the other terminal of the divider through the small resistor 29!. Thus, when the push button switch I32 and/or contactor I5I is closed, the cathode I93 of the valve I95 is con nected to both sides of the voltage divider I91 and charging of the capacitor I89 is halted. The capacitor I89 then discharges through an adjustable resistor 293 in parallel therewith. The negative plate of the capacitor I99 is connected to the grid I9I of the valve I 95 so that the valve remains non-conductive while the capacitor is charged. However, when the capacitor I85 becomes discharged after an interval of time determined by the setting of the resistor 293. the valve I95 is rendered conductive. Current then flows from one terminal of the voltage divider 331 through the operating coil 295 of the relay I49. a current'limiting resistor 201 to the anode of 299 of the valve I95. The circuit continues from the cathode I93 of the valve I95 through the contactor I5I to the other side of the divider. Thus, a predetermined time interval after the push button I32 is first closed. the relay I49 is energized and one of its contactors IE5 maintains the capacitor I55 of the timing system I99 discharged while the other contactor I41 breaks one ogzthe holding circuits around push button switch I To initiate a welding operation, the push button switch I32 is manually closed. Voltage divider IE3 is then energized, and after a time delay, the relay M3 is operated to close the circuit through the discharge device I35. During the time delay. the control capacitor I3I and the other capacitor I55 are charged. When the circuit through the device I36 is closed by the contactor MI. the device I36 immediately becomes conductive to discharge the control capacitor I32. The control capacitor I3I discharges to below the arcdrop 01' device I36 in a short but definite time interval, and the device I36 becomes nn-conduclive. Immediately thereafter, recharging oi the control capacitor I3I begins. However, when the control capacitor ISI is discharged, the control valve It! becomes conductive to conduct cur rent in each positive half period of the source. The operating coil ITI oi the control relay H is thus energized and maintained energized be-- tween positive hall periods by capacitor H3. As the control capacitor I3I rccliarges, it eventualh risz-s above the critical potential of the centre! valve iBI. However. the contactor '39 cf the relay 'II' is closed. the potential of the upper por- .lOIl l8? ol the divider 55 is placed across the mid i233 and cathode US of the contmi valv Iii: to maintain it conductive in positive liali periods of the alternating current.

After the contactor 69 of the control relay H is closed, the start valve 51 is rendered Conductive at the beginning of the next positive half period of the alternating current by the impulse received through the phase shifting circuit 82. As a re suit, the firing tube 3| of the first ignitron 5 becomes conductive to render the ignitron 5 conductive. The follow-up system causes the second ignitron I to conduct current during the negative half period of the source. The ignitrons 5 and I thus conduct current in alternate half periods until the stop valve 84 becomes conductive a predetermined time later. When the stop valve B l becomes conductive, the grid IIH of the firing tube 3! for the first ignitron 5 becomes negative and further conduction of current through the ignitron 5 is halted.

The potential impressed from the divider 55 on the control circuit of the control valve I8I is greatly reduced when the stop valve 84 becomes conductive. Since the control capacitor I 3i has been recharged in the meantime. the control valve IBI no longer conducts current in each positive half period. Consequently, the relay H is deenergized, opening the ccntactor 69 in the anode circuits of the start and stop valves 51 and 83 and closing a contactor 2H in a discharge circuit of the capacitor 93.

When the control relay II is first energized, its lower contactor i6] closes the discharging circuit of the capacitor H5 in the control circuit of the discharge device I36. While this capacitor I55 is maintained in a discharged condition, the device I36 cannot become conductive so that re charging of the control capacitor I3I may proceed without interruption. However, when the control relay 'II is again deenergized, the discharging circuit of the capacitor I55 is opened and recharging thereof at a selected rate is initiated. Upon charging the capacitor I55 to a potential above the critical potential of the device 636, the latter is again rendered conductive to discharge the control capacitor HH and effect energization of the relay II to start another cycle of operation.

When the push button switch I32 is initially closed, the precharged capacitor I89 in the overall timing system I begins to discharge at a predetermined rate depending upon the setting of the resistors 203 in parallel therewith. Resistor 203 is adjusted so that the capacitor potential drops to a point permitting firing of the valve I after a predetermined number of cycles of charging and discharging the control capacitor I3I. When the valve I95 becomes conductive, the relay I49 is energized and its contactor I65 closes the discharging circuit of the capacitor I55 and maintains the capacitor I55 in a discharged condition. As a result, further operation of the timing system I09 is prevented. Energization of relay I49 also opens contaetor I41 to deenergize relay I43 whose contactor I5I breaks one of the holding circuits around switch I32. The other holding circuit is completed through contactor I53 of control relay II so that the welding operation may not be halted in the middle of a welding impulse.

Although We have shown and described a specific embodiment of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. For use in supplying current from a source to a load, the combination comprising valve means for controlling the flow of current to the load, a first timing means effective while conditioned for operation to render said valve means conductive throughout a first preselected time interval, control means for conditioning said first timing means for operation, means for momentarily energizing said control means, means associated with said first timing means and said energizing means for maintaining said control means energized until the expiration of said first time interval, and a second timing means re sponsive to deenergization of said control means for initiating reoperation of said energizing means a second preselected time interval thereafter.

2. For use in supplying current from a source of periodic potential to a load, the combination comprising valve means for controlling the flow of current to the load, a first timing means efiective while conditioned for operation to render said valve means conductive throughout a first preselected time interval beginning at a predetermined instant in the period of said source following a conditioning thereof, control means for conditioning said first timing means for operation, means for energizing said control means throughout a second time interval shorter than said first time interval, a second timing means responsive to deenergization of said control means for initiating reoperation of said energizing means a second preselected time interval thereafter, and means associated with said first timing means and said energizing means for maintaining said control means energized until the expiration of said first time interval.

3. For use in supplying current from a source to a load, the combination comprising valve means for controlling the flow of current to the load, a first timing means effective while conditioned for operation to render said valve means conductive throughout a first preselected time interval, control means for conditioning said first timing means for operation, a normally charged capacitor, means for momentarily discharging said capacitor, means for energizing said control means when said capacitor is discharged, means in circuit with said capacitor constantly tending to charge it, means associated with said first timing means and said energizing means for maintaining said control means energized until the expiration of said first time interval, and a second timing means responsive to deenergization of said control means for initiating reoperation of said discharging means a second preselected time interval thereafter.

4. For use in supplying current from a source of periodic potential to a load, the combination comprising valve means for controlling the flow of current to the load, a first timing means effective while conditioned for operation to render said valve means conductive throughout a first preselected time interval beginning at a predetermined instant in the period of said source following a conditioning thereof, control means for conditioning said first timing means for operation, a normally charged capacitor, means for momentarily discharging said capacitor, means for energizing said control means when said capacitor is discharged, means in circuit with said capacitor constantly tending to charge it, means associated with said first timing means and said energizing means for maintaining said control means energized until the expiration of said first time interval, and a second timing means responsive to deenergization of said control means for initiating reoperation of said discharging means a second preselected time interval thereafter.

5. For use in supplying current from a source of periodic potential to a load, the combination comprising valve means for controlling the flow of current to the load, a first timing means effective While conditioned for operation to render said valve means conductive throughout a first preselected time interval beginning at a predetermined instant in the period of said source following a conditioning thereof, control means for conditioning said first timing means for operation, a capacitor, means constantly tending to charge said capacitor, means for momentarily discharging said capacitor, potential responsive means in circuit with said capacitor for energizing said control means while said capacitor is discharged, means associated with said first timing means for impressing a potential on said potential responsive means to maintain said control means energized until the expiration of said first time interval, and a second timing means responsive to deenergization of said control means for initiating reoperation of said discharging means a second preselected time interval thereafter.

6. For use in supplying power from a source of current to a load, the combination comprising valve means for controlling the flow of current to the load, timing means for rendering said valve means conductive throughout a preselected interval of time, control means for said timing means, means including a normally charged capacitor for impressing on said control means a. potential having one polarity with respect to a predetermined reference plane of potential, said control means being operable to initiate operation of said timing means when the impressed potential is changed to the opposite polarity with respect to said reference plane, means for momentarily discharging said capacitor to change the magnitude of said impressed potential and thereby change the impressed potential to said opposite polarity, means constantly tending to charge said capacitor and thereby return said impressed potential to said one polarity, a second timing means under the control of said control means for effecting reoperation of said discharging means a preselected time after the impressed potential returns to said one polarity, and means associated with said first timing means for preventing the impressed potential from returning to said one polarity until the instant of expiration of said first preselected time interval.

'7. Apparatus according to claim 6 in which the preventing means comprises means for supplying an additional potential from said first timing means to said control means during said first preselected time interval, said additional potential being of such magnitude and polarity as to prevent the resultant potential impressed on said control means from returning to said one polarity.

ROBERT W. PEARSON. CLARENCE B. STADUM. 

